Biosensor Chip Research Articles

Activation of pro-survival metabolic networks by 1,25(OH)2D3 does not hamper the sensitivity of breast cancer cells to chemotherapeutics

BackgroundWe have previously identified 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the bioactive form of vitamin D3, as a potent regulator of energy-utilization and nutrient-sensing pathways in prostate cancer cells. In the current study, we investigated the effects of 1,25(OH)2D3 on breast cancer (BCa) cell metabolism using cell lines representing distinct molecular subtypes, luminal (MCF-7 and T-47D), and triple-negative BCa (MDA-MB-231, MDA-MB-468, and HCC-1143).Methods1,25(OH)2D3’s effect on BCa cell metabolism was evaluated by employing a combination of real-time measurements of glycolysis/oxygen consumption rates using a biosensor chip system, GC/MS-based metabolomics, gene expression analysis, and assessment of overall energy levels. The influence of treatment on energy-related signaling molecules was investigated by immunoblotting.ResultsWe show that 1,25(OH)2D3 significantly induces the expression and activity of the pentose phosphate pathway enzyme glucose-6-phosphate dehydrogenase (G6PD) in all BCa cell lines, however differentially influences glycolytic and respiratory rates in the same cells. Although 1,25(OH)2D3 treatment was found to induce seemingly anti-oxidant responses in MCF-7 cells, such as increased intracellular serine levels, and reduce the expression of its putative target gene thioredoxin-interacting protein (TXNIP), intracellular reactive oxygen species levels were found to be elevated. Serine accumulation in 1,25(OH)2D3-treated cells was not found to hamper the efficacy of chemotherapeutics, including 5-fluorouracil. Detailed analyses of the nature of TXNIP’s regulation by 1,25(OH)2D3 included genetic and pharmacological inhibition of signaling molecules and metabolic enzymes including AMP-activated protein kinase and G6PD, as well as by studying the ITCH (E3 ubiquitin ligase)-TXNIP interaction. While these investigations demonstrated minimal involvement of such pathways in the observed non-canonical regulation of TXNIP, inhibition of estrogen receptor (ER) signaling by tamoxifen mirrored the reduction of TXNIP levels by 1,25(OH)2D3, demonstrating that the latter’s negative regulation of ER expression is a potential mechanism of TXNIP modulation.ConclusionsAltogether, we propose that regulation of energy metabolism contributes to 1,25(OH)2D3’s anti-cancer effects and that combining 1,25(OH)2D3 with drugs targeting metabolic networks in tumor cells may lead to synergistic effects.

An ultrasensitive biosensing flexible chip using a novel silver@Prussian blue core-shell nanocube composite

A real-time, portable, ultrahigh sensitive and selective biosensing chip is desired to satisfy the urgent requirement of the practical application. In this study, a novel three-dimensional (3D) silver nanocubes@Prussian blue (AgNCs@PB) core-shell material has been designed to develop an ultrasensitive biosensing chip by a seed-mediated interfacial assembly approach. A Prussian blue (PB) shell with the 30.12 nm thickness was precisely controlled to in-situ grow on the whole surface of AgNCs through the electrostatic interaction. A flexible and portable biosensing chip was printed and functionalized by using this 3D AgNCs@PB biosensing material to integrate the superior conductivity from AgNCs and electrocatalytic activity from PB for the remarkable performance enhancement. This chip can realize about four times increase of the sensitivity compared with the other PB based screen-printing electrode (SPE), as well as a very wide linear response from 0.01 mM to 1.3 mM and an ultralow limit of detection (LOD) of 0.005 mM for the glucose detection with an excellent anti-interference ability. Especially, it also presented an ultra-accurate detection of the blood sugar in a real serum with a low deviation (3.37%).

A 5-to-8-GHz Wideband Miniaturized Dielectric Spectroscopy Chip With <inline-formula> <tex-math notation="LaTeX">$I/Q$ </tex-math> </inline-formula> Mismatch Calibration in 65-nm CMOS

This paper presents a fully integrated broadband biosensor chip for miniaturized dielectric spectroscopy (DS). The proposed biosensor chip consists of wideband exciting signal source and high sensitivity receiver. The exciting signal source consists of a wideband phase-locked loop (PLL) and output drivers. The wideband receiver is composed of low noise amplifier, mixer, and output buffers. The proposed receiver with in-phase ( ${I}$ ) and quadrature-phase ( ${Q}$ ) signals mismatch calibration measures the frequency-dependent S21 magnitude and phase of a microfluidic dielectric sensor. The DS system implements a modified frequency response analysis by converting the biosensor response signal from the RF excitation frequency to low frequency using a passive mixer. Dielectric measurements results of ethanol with the proposed biosensor chip in the range of 5–8 GHz are in excellent agreement (error <1%) with theoretical values. The chip is fabricated in 65-nm CMOS process. The total power consumption is 18 mW with 1.2-V supply.

Top-down and sensitive indium oxide nanoribbon field effect transistor biosensor chips integrated with on-chip gate electrodes toward point of care applications

We report a scalable, uniform, and sensitive top-down fabricated indium oxide (In2O3) nanoribbon biosensor platform with integrated on-chip gate electrodes using two photolithographic masks. The purpose of this on-chip gate electrode is to control the operational point of the sensor during biomolecular detection replacing the cumbersome external Ag/AgCl electrode. It exhibits excellent capability in gating transistors in an aqueous condition and high stability during the sensing experiment, which is similar to the Ag/AgCl electrode. Its compactness increases the portability and pushes this platform toward a practical use. To demonstrate its capability for detection of biomolecules, we combine this platform with the electronic enzyme-linked immunosorbent assay (ELISA) technique to amplify the signal and to bypass limitation of the Debye screening effect from high salt concentration of physiological samples. Troponin I, a cardiac marker for diagnosis of acute myocardial infarction (AMI), was selected as the target molecule in this study. The In2O3 nanoribbon device offers a high response of 30% toward 0.1 pg ml−1 troponin I concentration and a lower detection limit than that of the commercial ELISA kit on the market by five orders of magnitude. The total assay time from the sample collection to the data acquisition is about 45 min, which is within the constraint of the emergency care application. With the demonstrated sensitivity, uniformity, scalability, quick turn-around time and ability to be integrated, our In2O3 nanoribbon biosensor platform has high potential toward clinical tests for early diagnosis of AMI.

Enzymatic removal of protein fouling from self-assembled cellulosic nanofilms: experimental and modeling studies.

Protein fouling is a serious problem in many food, pharmaceutical and household industries. In this work, the removal of rubisco protein fouling fromcellulosic surfaces using a protease (subtilisin A) has been investigated experimentally and mathematically. The cellulosic surfaces were prepared using self-assembled monolayers (SAMs) on a surface plasmon resonance biosensor (chip) surface after conjugating cellulose to α-lipoic acid. Rubisco adsorption on the prepared cellulosic SAMs was found to be irreversible, leading to the creation of a tough protein fouling. The heterogeneous enzymatic cleansing of such tough fouling involves enzyme transfer to the surface and the subsequent removal of the rubisco via protease activity. In this work, these two processes were decoupled, allowing enzyme transfer and enzymaticsurface reaction to be parameterized separately. Mathematical modeling of the enzymatic cleaning of protein fouling from cellulosic SAMs revealed that enzymatic mobility at the interface is an important factor. The approach presented in this work might be useful in designing better protein fouling-resistant surfaces. It could also be used to guide efforts to screen and gauge the cleaning performance of detergent-enzyme formulations.

Epitope Ligand Binding Sites of Blood Group Oligosaccharides in Lectins Revealed by Pressure-Assisted Proteolytic Excision Affinity Mass Spectrometry.

Affinity mass spectrometry using selective proteolytic excision and extraction combined with MALDI and ESI mass spectrometry has been applied to the identification of epitope binding sites of lactose, GalNac, and blood group oligosaccharides in two blood group-specific lectins, human galectin-3 and glycine max lectin. The epitope peptides identified comprise all essential amino acids involved in carbohydrate recognition, in complete agreement with available X-ray structures. Tryptic and chymotryptic digestion of lectins for proteolytic extraction/excision-MS was substantially improved by pressure-enhanced digestion using an automated Barocycler procedure (40kpsi). Both previously established immobilization on affinity microcolumns using divinyl sulfone and coupling of a specific peptide glycoprobe to the gold surface of a biosensor chip were successfully employed for proteolytic excision and extraction of carbohydrate epitopes and affinity measurements. The identified epitope peptides could be differentiated according to the carbohydrate employed, thus demonstrating the specificity of the mass spectrometric approach. The specificities of the epitope ligands for individual carbohydrates were further ascertained by affinity studies using synthetic peptide ligands with immobilized carbohydrates. Binding affinities of the synthetic ligand peptides to lactose, in comparison to the intact full-length lectins, were determined by surface acoustic wave (SAW) biosensor analysis and provided micromolar KD values for the intact lectins, in agreement with results of previous ITC and SPR studies. Binding affinities of the epitope peptides were approximately two orders of magnitude lower, consistent with their smaller size and assembled arrangement in the carbohydrate recognition domains. Graphical Abstract ᅟ.

On-chip membrane protein cell-free expression enables development of a direct binding assay: A curious case of potassium channel KcsA-Kv1.3

Despite the significant role integral membrane proteins (IMPs) play in the drug discovery process, it remains extremely challenging to express, purify, and in vitro stabilize them for detailed biophysical analyses. Cell-free transcription-translation systems have emerged as a promising alternative for producing complex proteins, but they are still not a viable option for expressing IMPs due to improper post-translational folding of these proteins. We have studied key factors influencing in vitro folding of cell-free-expressed IMPs, particularly oligomeric proteins (i.e., ion channels). Using a chimeric ion channel, KcsA-Kv1.3 (K-K), as a model IMP, we have investigated several physiochemical determinants including artificial bilayer environments (i.e., lipid, detergent) for K-K in vitro stabilization. We observed that fusion of a ‘superfolder’ green fluorescent protein (sfGFP) to K-K as a protein expression reporter not only improves the protein yield, but surprisingly facilitates the K-K tetramer formation, probably by enhancing the solubility of monomeric K-K. Additionally, anionic lipids (i.e., DMPG) were found to be essential for the correct folding of cell-free-expressed monomeric K-K into tetramer, underscoring the importance of lipid-protein interaction in maintaining structural-functional integrity of ion channels. We further developed methods to integrate cell-free-expressed IMPs directly onto a biosensor chip. We employed a solid-supported lipid bilayer onto the surface plasmon resonance (SPR) chip to insert nascent K-K in a membrane. In a different approach, an anti-GFP-functionalized surface was used to capture in situ expressed K-K via its sfGFP tag. Interestingly, only the K-K-functionalized capture surface prepared by the latter strategy was able to interact with K-K's small binding partners. This generalizable approach can be further extended to other membrane proteins for developing direct binding assays involving small ligands.

Enhancement of local surface plasmon resonance (LSPR) effect by biocompatible metal clustering based on ZnO nanorods in Raman measurements

The development of size-selective and non-destructive detection techniques for nanosized biomarkers has many reasons, including the study of living cells and diagnostic applications. We present an approach for Raman signal enhancement on biocompatible sensing chips based on surface enhancement Raman spectroscopy (SERS). A sensing chip was fabricated by forming a ZnO-based nanorod structure so that the Raman enhancement occurred at a gap of several tens to several hundred nanometers. The effect of coffee-ring formation was eliminated by introducing the porous ZnO nanorods for the bio-liquid sample. A peculiarity of this approach is that the gold sputtered on the ZnO nanorods initially grows at their heads forming clusters, as confirmed by secondary electron microscopy. This clustering was verified by finite element analysis to be the main factor for enhancement of local surface plasmon resonance (LSPR). This clustering property and the ability to adjust the size of the nanorods enabled the signal acquisition points to be refined using confocal based Raman spectroscopy, which could be applied directly to the sensor chip based on the optimization process in this experiment. It was demonstrated by using common cancer cell lines that cell growth was high on these gold-clad ZnO nanorod-based surface-enhanced Raman substrates. The porosity of the sensing chip, the improved structure for signal enhancement, and the cell assay make these gold-coated ZnO nanorods substrates promising biosensing chips with excellent potential for detecting nanometric biomarkers secreted by cells.

Producing Covalent Microarrays of Amine‐Conjugated DNA Probes on Various Functional Surfaces to Create Stable and Reliable Biosensors

AbstractOligonucleotide‐based microarrays are ideal tools for genetic testing and diagnostics due to their stability, ease of synthesis, and high specificity for the target of interest. This study reports on the effectiveness of several coupling strategies to covalently attach single‐stranded nucleic acids to surfaces, focusing on the robustness of the attachment in various environmental conditions, such as pH and temperature. Various characteristics of DNA microarrays produced using amine‐conjugated DNA probes on five different functional surfaces, commonly used for immobilization of biomolecules, namely, epoxy, carboxyl, amine, aldehyde, and N‐hydroxysuccinimide‐coated substrates, are investigated. Immobilization efficiency, changes in surface energy, as well as the stability of the conjugated DNA upon exposure to various environmental conditions are measured. Finally, in order to study the postimmobilization viability of the developed biosensors, microarrays of synthetic RNA cleaving probes (DNAzyme) are immobilized onto these surfaces and their functionality is evaluated through their ability to detect Escherichia coli at various temperatures. Results show that epoxy‐coated plastic surfaces are most ideal for the creation of DNA‐based biosensing chips. This study provides a guideline for producing oligonucleotide‐based microarrays on glass and plastic substrates and can be used for developing microarray‐based biosensors, suitable for long‐term storage.

Wireless poly(dimethylsiloxane) quartz-crystal-microbalance biosensor chip fabricated by nanoimprint lithography for micropump integration aiming at application in lab-on-a-chip

We developed a quartz-crystal-microbalance (QCM) biosensor chip that operates wirelessly via electromagnetic waves, using poly(dimethylsiloxane) (PDMS). An AT-cut quartz oscillator (22–30 µm) is packaged in a microchannel, where it is supported by micropillars without mechanical fixing. As a result, the quartz oscillator is little affected by the thermal stress caused by the difference in the thermal expansion coefficients of the components, and the leakage of the vibration energy of the quartz oscillator is reduced. Consequently, high-frequency (∼56 MHz) measurement with a stable baseline (±∼2 ppm) is realized. We succeeded in repeatedly monitoring the binding reaction between immunoglobulin G (IgG) and Staphylococcus aureus protein A (SPA) with the quartz oscillator on which SPA molecules were immobilized nonspecifically. In addition, the affinity between SPA and IgG was calculated from the association and dissociation curves, and the usefulness of our wireless PDMS QCM biosensor was demonstrated.

Gating Hysteresis as an Indicator for Silicon Nanowire FET Biosensors

We present a biosensor chip with integrated large area silicon nanowire-based field effect transistors (FET) for human α-thrombin detection and propose to implement the hysteresis width of the FET transfer curve as a reliable parameter to quantify the concentration of biomolecules in the solution. We further compare our results to conventional surface potential based measurements and demonstrate that both parameters distinctly respond at a different analyte concentration range. A combination of the two approaches would provide broader possibilities for detecting biomolecules that are present in a sample with highly variable concentrations, or distinct biomolecules that can be found at very different levels. Finally, we qualitatively discuss the physical and chemical origin of the hysteresis signal and associate it with the polarization of thrombin molecules upon binding to the receptor at the nanowire surface.

Measuring the Adhesion Forces for the Multivalent Binding of Vancomycin-Conjugated Dendrimer to Bacterial Cell-Wall Peptide.

Multivalent ligand-receptor interaction provides the fundamental basis for the hypothetical notion that high binding avidity relates to the strong force of adhesion. Despite its increasing importance in the design of targeted nanoconjugates, an understanding of the physical forces underlying the multivalent interaction remains a subject of urgent investigation. In this study, we designed three vancomycin (Van)-conjugated dendrimers G5(Van) n ( n = mean valency = 0, 1, 4) for bacterial targeting with generation 5 (G5) poly(amidoamine) dendrimer as a multivalent scaffold and evaluated both their binding avidity and physical force of adhesion to a bacterial model surface by employing surface plasmon resonance (SPR) spectroscopy and atomic force microscopy. The SPR experiment for these conjugates was performed in a biosensor chip surface immobilized with a bacterial cell-wall peptide Lys-d-Ala-d-Ala. Of these, G5(Van)4 bound most tightly with a KD of 0.34 nM, which represents an increase in avidity by 2 or 3 orders of magnitude relative to a monovalent conjugate G5(Van)1 or free vancomycin, respectively. By single-molecule force spectroscopy, we measured the adhesion force between G5(Van) n and the same cell-wall peptide immobilized on the surface. The distribution of adhesion forces increased in proportion to vancomycin valency with the mean force of 134 pN at n = 4 greater than 96 pN at n = 1 at a loading rate of 5200 pN/s. In summary, our results are strongly supportive of the positive correlation between the avidity and adhesion force in the multivalent interaction of vancomycin nanoconjugates.

A film-based integrated chip for gene amplification and electrochemical detection of pathogens causing foodborne illnesses

Given the increased interest in public hygiene due to outbreaks of food poisoning, increased emphasis has been placed on developing novel monitoring systems for point-of-care testing (POCT) to evaluate pathogens causing foodborne illnesses. Here, we demonstrate a pathogen evaluation system utilizing simple film-based microfluidics, featuring simultaneous gene amplification, solution mixing, and electrochemical detection. To minimize and integrate the various functionalities into a single chip, patterned polyimide and polyester films were mainly used on a polycarbonate housing chip, allowing simple fabrication and alignment, in contrast to conventional polymerase chain reaction, which requires a complex biosensing system at a bench-top scale. The individual integrated sensing chip could be manually fabricated in 10 min. Using the developed film-based integrated biosensing chip, the genes from the pathogens causing foodborne illnesses were simultaneously amplified based on multiple designed microfluidic chambers and Hoechst 33258, which intercalates into double-stranded DNA, to generate the electrochemical signal. The target pathogen gene was accurately analyzed by square wave voltammetry (SWV) within the 25 s, while the gel electrophoresis required about 30 min. Based on the developed integrated biosensing chip, the 1.0 × 101 and 1.0 × 102 colony-forming unit (CFU) of Staphylococcus aureus and Escherichia coli were sensitively detected with high reproducibility in the 25 s. On the basis of the significant features of the film-based molecular analysis platform, we expect that the developed sensor could be applied to the screening of various pathogens as a POCT device.

Monitoring of bacteria biofilms forming process by in-situ impedimetric biosensor chip

A biosensor chip integrated interdigital microelectrodes was proposed and applied to monitor the formation process of Salmonella and E. coli biofilms in this paper. The biosensor chip was composed of a glass substrate with interdigital microelectrodes and PDMS layer with micro cavities. The electrochemical impedance spectroscopy (EIS) of Salmonella and E. coli biofilms was measured by the biosensor chip using alternating voltage of 100 mv in the frequency range from 1 Hz to 100 kHz for 48 h. It was illustrated that the changes of impedance spectroscopy of biofilms occurred with culture time. Furthermore, impedance spectroscopy of biofilms was fitted by an equivalent circuit model including the biofilms capacitance (Cb) and the biofilms resistance (Rb) parameters. The results indicated that the Cb presented a tendency to decrease first and then rise with culture time, while the Rb was in the opposite direction. These changing trends were consistent with the formation process of biofilms that bacteria adhered to electrodes surface, and then formed mature biofilms, finally escaped from biofilms. In addition, it was also demonstrated that the changing trends of Cb and Rb with culture time were quite different between Salmonella and E. coli. The results obtained by impedance detection were in accordance with the results of using crystal violet staining to analyze biofilms formation process, under the same conditions for bacterial culture. The biosensor chip provided a promising platform for further study of biofilms owing to its unique advantages of real time, continuity, and non-invasion for bacteria biofilms detection and in-situ monitoring.

A label-free cellulose SERS biosensor chip with improvement of nanoparticle-enhanced LSPR effects for early diagnosis of subarachnoid hemorrhage-induced complications

It is very difficult to predict some complications after subarachnoid hemorrhage (SAH), despite rapid advances in medical science. Herein, we introduce a label-free cellulose surface-enhanced Raman spectroscopy (SERS) biosensor chip with pH-functionalized, gold nanoparticle (AuNP)-enhanced localized surface plasmon resonance (LSPR) effects for identification of SAH-induced cerebral vasospasm and hydrocephalus caused by cerebrospinal fluid (CSF). The SERS biosensor chip was implemented by the synthesis reaction of the AuNPs, which were charged positively through pH level adjustment, onto a negatively-charged cellulose substrate with ξ = –30.7 mV. The zeta potential, nanostructural properties, nanocrystallinity, and computational calculation-based electric field distributions of the cellulose-originated AuNPs were optimized to maximize LSPR phenomena and then characterized. Additionally, the performance of the SERS biosensor was compared under two representative excitation laser sources in the visible region (532 nm) and near-infrared region (785 nm). The Raman activities of our SERS biosensor chip were evaluated by trace small molecules (crystal violet, 2 µL), and the biosensor achieved an enhancement factor of 3.29 × 109 for the analytic concept with an excellent reproducibility of 8.5% relative standard deviation and a detection limit of 0.74 pM. Furthermore, the experimental results revealed that the five proposed SERS-based biomarkers could provide important information for identifying and predicting SAH-induced cerebral vasospasm and hydrocephalus complications (91.1% reliability and 19.3% reproducibility). Therefore, this facile and effective principle of our SERS biosensor chip may inspire the basis and strategies for the development of sensing platforms to predict critical complications in various neurosurgical diagnoses.

Reliable Strategy for Analysis of Complex Biosensor Data

When using biosensors, analyte biomolecules of several different concentrations are percolated over a chip with immobilized ligand molecules that form complexes with analytes. However, in many cases of biological interest, e.g., in antibody interactions, complex formation steady-state is not reached. The data measured are so-called sensorgram, one for each analyte concentration, with total complex concentration vs time. Here we present a new four-step strategy for more reliable processing of this complex kinetic binding data and compare it with the standard global fitting procedure. In our strategy, we first calculate a dissociation graph to reveal if there are any heterogeneous interactions. Thereafter, a new numerical algorithm, AIDA, is used to get the number of different complex formation reactions for each analyte concentration level. This information is then used to estimate the corresponding complex formation rate constants by fitting to the measured sensorgram one by one. Finally, all estimated rate constants are plotted and clustered, where each cluster represents a complex formation. Synthetic and experimental data obtained from three different QCM biosensor experimental systems having fast (close to steady-state), moderate, and slow kinetics (far from steady-state) were evaluated using the four-step strategy and standard global fitting. The new strategy allowed us to more reliably estimate the number of different complex formations, especially for cases of complex and slow dissociation kinetics. Moreover, the new strategy proved to be more robust as it enables one to handle system drift, i.e., data from biosensor chips that deteriorate over time.

Superior Sensitivity of Copper-Based Plasmonic Biosensors.

Plasmonic biosensing has been demonstrated to be a powerful technique for quantitative determination of molecular analytes and kinetic analysis of biochemical reactions. However, interfaces of most plasmonic biosensors are made of noble metals, such as gold and silver, which are not compatible with industrial production technologies. This greatly limits biosensing applications beyond biochemical and pharmaceutical research. Here, we propose and investigate copper-based biosensor chips fully fabricated with a standard complementary metal-oxide-semiconductor (CMOS) process. The protection of thin copper films from oxidation is achieved with SiO2 and Al2O3 dielectric films deposited onto the metal surface. In addition, the deposition of dielectric films with thicknesses of only several tens of nanometers significantly improves the biosensing sensitivity, owing to better localization of electromagnetic field above the biosensing surface. According to surface plasmon resonance (SPR) measurements, the copper biosensor chips coated with thin films of SiO2 (25 nm) and Al2O3 (15 nm) show 55% and 75% higher sensitivity to refractive index changes, respectively, in comparison to pure gold sensor chips. To test biomolecule immobilization, the copper-dielectric biosensor chips are coated with graphene oxide linking layers and used for the selective analysis of oligonucleotide hybridization. The proposed plasmonic biosensors make SPR technology more affordable for various applications and provide the basis for compact biosensors integrated with modern electronic devices.

Electrically-receptive and thermally-responsive paper-based sensor chip for rapid detection of bacterial cells

Although significant technological advancements have been made in the development of analytical biosensor chips for detecting bacterial strains (E. coli, S. Mutans and B. Subtilis), critical requirements i.e. limit of detection (LOD), fast time of response, ultra-sensitivity with high reproducibility and good shelf-life with robust sensing capability have yet to be met within a single sensor chip. In order to achieve these criteria, we present an electrically-receptive thermally-responsive (ER-TR) sensor chip comprised of simple filter paper used as substrate coated with composite of poly(N-isopropylacrylamide) polymer (PNIPAm) – graphene nanoplatelet (GR) followed by evaporation of Au electrodes for capturing both Gram-positive (S. mutans and B. subtilis) and Gram-negative (E. coli) bacterial cells in real-time. Autoclave water, tap water, lake water and milk samples were tested with ER-TR chip with and without bacterial strains at varying concentration range 101–105 cells/mL. The sensor was integrated with in-house built printed circuit board (PCB) to transmit/receive electrical signals. The interaction of E. coli, S. mutans and B. subtilis cells with fibers of PNIPAm-GR resulted in a change of electrical resistance and the readout was monitored wirelessly in real-time using MATLAB algorithm. Finally, prepared ER-TR chip exhibited the reproducibility of 85–97% with shelf-life of up to four weeks after testing with lake water sample.

Multiwalled carbon nanotube modified microfluidic-based biosensor chip for nucleic acid detection

An impedimetric microfluidic–based biosensor was fabricated and investigated for quantification of the DNA sequence specific to chronic myelogenous leukemia (CML). The sensor chip was constructed by electrophoretic deposition of carboxyl-modified multiwalled carbon nanotubes (MWCNT) on the patterned (via wet chemical etching method) indium–tin–oxide (ITO) coated glass substrate. The MWCNT surface was immobilized with CML specific deoxyribonucleic acid probe, followed by sealing of the biochip with poly (dimethylsiloxane) microchannel for fluid control. This integrated miniaturized system was used to monitor complementary target DNA concentration by measuring the interfacial charge transfer resistance via hybridization. The presence of complementary DNA in buffer solution resulted in significant decrease in electrical conductivity of the interface thereby presenting a barrier for transport of the redox probe ions. Under optimal conditions, this microfluidic biochip exhibited good calibration range from 1fM to 1 μM and a response time of 60 s.

Design and simulation of MEMS microvalves for silicon photonic biosensor chip

For the early and easy diagnosis of diseases, we have proposed a silicon photonic biosensor chip with two kinds of MEMS microvalves for a multiple-item detection system. The driving voltage of the vertical type with the circular-plate capacitor structure and that of the lateral type with the comb-shaped electrode are investigated. From mechanical calculations, the driving voltage of the vertical type is estimated to be 30 V and that of the lateral type to be 15 V. The propagation loss at the intersecting waveguides of arrayed ring-resonator biosensors is also estimated. In the case of optimized intersecting waveguides, more than 67% transmittance of TE-mode light is simulated for the series connection of 20 intersecting waveguides. It is confirmed that it is possible to fabricate an 8 × 12 arrayed biosensor chip in an area of 1 × 1.5 mm2 taking the device size of the microvalves into consideration. We have, for the first time, designed a whole system, including sensors and a fluid channel with MEMS microvalves.